We have developed a new method for determining the approximate magnetic flux content of various solar wind structures in the ecliptic plane, using single-spacecraft measurements. The two-dimensional magnetic flux in a region of the solar wind is given by the integral of the radial magnetic field component over an arc perpendicular to the radial. Unfortunately, such measurements cannot be achieved with single (or even several) spacecraft in the solar wind. We will show that the desired two-dimensional, ecliptic plane magnetic flux integral, at least for regions with simple magnetic topologies, is equivalent to ϕ=∫By‖v‖dt, where By is the ecliptic plane field component perpendicular to the solar wind velocity vector v. Thus ϕ can be determined entirely from measured quantities. In this study we examine variations in the magnetic flux in the ecliptic plane over a 16-year interval. In addition, we address the question of the opening and closing of interplanetary magnetic flux by comparing the ecliptic plane flux content of both coronal mass ejections (CMEs) and heat flux dropouts (HFDs). If CMEs remain at least partially attached to the Sun, they would serve to open new magnetic flux to the interplanetary medium.

In contrast, flux could be closed off by reconnection across helmet streamers in the corona, leading to the release of U-shaped magnetic structures open to the outer heliosphere at both ends and to the reture of closed arches to the Sun. One interpretation of HFDs in the solar wind halo electron population is that they represent the interplanetary signatures of such disconnected U-shaped structures. The ecliptic plane flux of CMEs is determined to be approximately 4 time greater than that of HFDs over the 18-month interval studied; complications of making such comparisons are discussed. ¿American Geophysical Union 1991